1. Technical Field
The present invention is directed to pistons for heavy duty diesel engine applications, and more particularly to the formation of such pistons having internal galleries for cooling oil.
2. Related Art
Piston structures having two closed galleries are known, for example, in U.S. Pat. Nos. 3,613,521; 4,581,983; 4,662,319; and 4,532,686.
In each of the patents, upper and lower crown parts are separately formed and then joined across mating surfaces to define an inner and outer chamber within the piston body. In U.S. Pat. No. 3,613,521, the crown parts are joined by brazing through provision of a gap at the bottom of annular grooves machined in the lower crown part in which annular ribs of the upper crown part are received. U.S. Pat. No. 4,581,983 joins the upper crown part to the lower crown part by means of charge carrier rays. U.S. Pat. No. 4,662,319 presents a complex arrangement of internal chambers and passages which would be extremely costly to produce. U.S. Pat. No. 4,532,686 provides dual chambers but which are not in fluid communication with one another for the flow of cooling oil from one chamber to the other.
It is an object of the present invention to improve upon dual gallery pistons to provide an efficient, robust piston structure.
According to a first aspect of the invention, an articulated piston assembly for heavy duty diesel engine applications is provided comprising a piston body including a one piece upper crown part and a one piece lower crown part in conjunction with an articulated piston skirt provided as a separate structure from the piston body. The upper crown part has a lower connecting portion formed with inner and outer annular ribs which are spaced from one another and extend axially to free ends each presenting a planar joining surface of the ribs. The lower crown part has an upper connecting portion from which a pair of pin boss portions depend having a space between them to receive a connecting rod. The upper connecting portion has inner and outer annular ribs extending axially to free ends thereof each presenting a planar joining surface of the lower crown part ribs. The lower crown part further has an inner gallery floor arranged above the space between the rib bosses and surrounded by the inner annular rib of the lower crown part. According to the invention, the inner and outer ribs of the upper and lower crown parts are joined across their respective joining surfaces by friction weld joints to define an inner and outer oil gallery within the joined crown parts separated by the inner ribs. The inner rib of the lower crown part is formed with at least one fluid transfer port spaced axially from the joining surface thereof and extending between the outer oil gallery and the inner oil gallery to establish fluid communication therebetween.
The inner gallery floor includes an opening establishing fluid communication between the inner gallery and the space between the pin bosses.
According to a further aspect of the invention, a monobloc piston assembly for heavy duty diesel engine applications is provided having one piece upper and lower crown parts sharing the same features as the articulated piston above, except that in place of the articulated piston skirt, the monobloc piston has a skirt which is formed as one piece with the pin bosses as an integral structure of the lower crown part.
The invention has the advantages of providing upper and lower crown parts joined by friction welding to define dual galleries within the piston structure to provide a high integrity connection between the upper and lower crown parts which is superior to brazing or charged carrier rays of the known prior art pistons above having communicating dual oil galleries.
The invention further provides a simple dual gallery structure which is highly effective at cooling the upper region of the piston with cooling oil that circulates within and between the chambers to extract heat from the piston.
Another advantage of the friction welding process employed in joining the upper and lower crown parts is that the inner and outer ribs can be friction welded simultaneously in a single operation.